Iron is essential for cell growth and division, but it is also harmful when it accumulates in cells. Therefore, the intracellular level of iron must be precisely regulated. Iron-overload diseases are primarily caused by hereditary hemochromatosis (HH)-the most common genetic disorder in Europe and the United States. The well studied pathways for regulated iron uptake and storage are mediated by the transferrin/transferrin receptor complex and by the storage protein, ferritin, respectively. However, it appears that novel proteins can regulate iron metabolism by interaction with the transferrin/transferrin receptor complex and with other proteins involved in transferrin-independent iron-uptake pathways. Recently, the gene responsible for HH was cloned and characterized as a novel major histocompatibility complex (MHC) class I-like gene (HFE) that is distinguishable from the wild type by a single mutation that prevents its transport to the cell surface. The HFE protein is known to regulate iron uptake possibly by interaction with the transferrin receptor. HFE transcripts are not detected in resting lymphocytes, but are present at high levels in human tumor cells, especially those of lymphoid origin, implying that HFE may play a role in tumorigenesis. In order to define the role of HFE in iron-homeostasis and to determine if interferences with its normal expression play a role in diseases such as cancer, we propose (a) to characterize cellular proteins that interact with HFE, (b) to investigate the intracellular trafficking of HFE and its complexes, and (c) to determine how extracellular factors (e.g. iron, cytokines, viral infections) as well as intracellular factors (e.g. chaperones, heat shock proteins, viral proteins) regulate the trafficking and/or recycling of HFE complexes. Ultimately, by determining just how the HFE molecule functions to aid the growth of cancer cells, we hopefully will be able to develop drugs that interfere with the process and result in cancer cell death. Due to its specific binding to transferrin receptor, our recent studies suggest that it may be possible to exploit soluble HFE as a specific vector for the intracellular delivery of drugs.